Inhibition of connexin hemichannels alleviates non-alcoholic steatohepatitis in mice

Background and aims: Connexins are the molecular constituents of gap junctions and hemichannels. In liver, connexin32 is the predominant connexin species expressed by hepatocytes, whereas non-parenchymal cells typically harbor connexin43. While gap junctions mediate intercellular communication and support liver homeostasis, hemichannels provide a circuit for paracrine signaling and are preferentially opened by pathological stimuli, including inflammation and oxidative stress. The latter are essential features of non-alcoholic steatohepatitis, being the most prevalent chronic liver disease in the Western world. In the present study, it was investigated whether hemichannels composed of connexin32 and connexin43 play a role in non-alcoholic steatohepatitis. Methods: Mice were fed a choline-deficient high-fat diet for 8 weeks. TAT-Gap24 or TAT-Gap19, specific inhibitors of hemichannels composed of connexin32 and connexin43, respectively, were administered for 2 weeks via an abdominal osmotic pump. Subsequently, a number of clinically relevant read-outs, including histopathological examination as well as various indicators of inflammation, liver damage and oxidative stress were tested. Channel specificity of TAT-Gap24 and TAT-Gap19 was tested in vitro by fluorescence recovery after photobleaching analysis and measurement of extracellular release of adenosine triphosphate. Whole transcriptome microarray analysis was performed on liver tissue. Results: TAT-Gap24 and TAT-Gap19 did reduce adenosine triphosphate release, but did not inhibit gap junctions. Diet-fed animals treated with TAT-Gap24 or TAT-Gap19 displayed decreased amounts of liver triglycerides and cholesterol, reduced quantities of inflammatory markers and augmented levels of superoxide dismutase in comparison with saline-treated counterparts. Furthermore, TAT-Gap19-treated diseased mice exhibited less fat weight and lower serum alanine aminotransferase quantities, while TAT-Gap24 decreased malondialdehyde levels. Expression of several genes related to inflammation, oxidative stress and lipid transport were differentially changed. Conclusion: These findings show for the first time the involvement of connexin32 and connexin43 hemichannels in non-alcoholic steatohepatitis and, simultaneously, suggest a role as potential drug targets in non-alcoholic steatohepatitis